Radiation-emitting devices are generally known and used for radiation therapy in the treatment of patients with cancers. Typically, a radiation therapy device includes a gantry which can be swiveled around a horizontal axis of rotation in the course of a therapeutic treatment. A linear accelerator is located in the gantry for generating a high-energy beam beam for therapy. This high radiation beam can be an electron radiation or photon (X-ray) beam. During treatment, the radiation beam is provided on one zone of a patient lying at the isocenter of gantry rotation.
The goal of radiation treatment planning is to maximize the dose to the target volume while protecting radiation sensitive healthy tissue.
A feature of radiation therapy involves portal images, which are commonly used to verify and record the patient tumor location. Portal images, i.e., images of the port through the patient through which radiation emerges, include manual (film) and electronic images (EPI) taken before, during or after the treatment. Electronic portal images (EPI), when taken before the treatment, give the therapist the opportunity of correcting for minor patient positioning errors. Portal images taken during treatment provide a means of monitoring patient movement. Further, EPI allows therapists to take images remotely without going inside the treatment room.
Because energy of the x-ray for radiotherapy is in thereat megavolt range, images acquired by the traditional film and EPI method in general show lack of details of the patient anatomy. One method of improving EPI image detail contrast is to control the analog to digital (A/D) window of the video capture device so that only part of video signal containing useful image information is digitized.
A conventional system used to control the A/D window has some deficiencies. A conventional method for analyzing the useful information in a particular image comprises constructing a histogram of the area to be imaged and analyzing that area by use of an algorithm. This histogram is plotted with dark pixel values on the left, bright pixels on the right. The analysis comprises determining a sharpest peak point on the left hand side of the histogram to determine the lower cutoff of the image. Typically the lower cutoff is at the nearest local minimum to the right of the sharpest peak. The highest peak on the right hand side of the histogram is then utilized to determine the upper cutoff. Typically the upper cutoff is at the nearest local minimum to the left of the highest peak.
This algorithm functions well with large amount of air and no high contrast objects in the field of view. However, if small amount of air or high contrast objects are in the field of view to the left of the true dark peak, the image of interest may be lost. The algorithm described above also produces dark or white washed images in an unpredictable manner. Finally, this algorithm requires user expertise to manipulate the "gain" and "black level" of the camera. Accordingly, a user can sometimes become frustrated when using the conventional algorithm.
Accordingly, what is needed is a method and system for controlling portal image acquisition and automatically capturing the EPI.